[RFC PATCH v3 6/7] mm/damon/paddr: introduce DAMOS_MIGRATE_HOT action for promotion

[Honggyu Kim]

From: Hyeongtak Ji <hyeongtak.ji@xxxxxx>

This patch introduces DAMOS_MIGRATE_HOT action, which is similar to
DAMOS_MIGRATE_COLD, but it is targeted to migrate hot pages.

It migrates pages inside the given region to the 'target_nid' NUMA node
in the sysfs.

Here is one of the example usage of this 'migrate_hot' action.

  $ cd /sys/kernel/mm/damon/admin/kdamonds/<N>
  $ cat contexts/<N>/schemes/<N>/action
  migrate_hot
  $ echo 0 > contexts/<N>/schemes/<N>/target_nid
  $ echo commit > state
  $ numactl -p 2 ./hot_cold 500M 600M &
  $ numastat -c -p hot_cold

  Per-node process memory usage (in MBs)
  PID             Node 0 Node 1 Node 2 Total
  --------------  ------ ------ ------ -----
  701 (hot_cold)     501      0    601  1101

Signed-off-by: Hyeongtak Ji <hyeongtak.ji@xxxxxx>
Signed-off-by: Honggyu Kim <honggyu.kim@xxxxxx>
---
 include/linux/damon.h    |  2 ++
 mm/damon/paddr.c         | 12 ++++++++++--
 mm/damon/sysfs-schemes.c |  4 +++-
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index df8671e69a70..934c95a7c042 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -105,6 +105,7 @@ struct damon_target {
  * @DAMOS_NOHUGEPAGE:	Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
  * @DAMOS_LRU_PRIO:	Prioritize the region on its LRU lists.
  * @DAMOS_LRU_DEPRIO:	Deprioritize the region on its LRU lists.
+ * @DAMOS_MIGRATE_HOT:  Migrate for the given hot region.
  * @DAMOS_MIGRATE_COLD: Migrate for the given cold region.
  * @DAMOS_STAT:		Do nothing but count the stat.
  * @NR_DAMOS_ACTIONS:	Total number of DAMOS actions
@@ -123,6 +124,7 @@ enum damos_action {
 	DAMOS_NOHUGEPAGE,
 	DAMOS_LRU_PRIO,
 	DAMOS_LRU_DEPRIO,
+	DAMOS_MIGRATE_HOT,
 	DAMOS_MIGRATE_COLD,
 	DAMOS_STAT,		/* Do nothing but only record the stat */
 	NR_DAMOS_ACTIONS,
diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index fe217a26f788..fd9d35b5cc83 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -229,6 +229,7 @@ static bool damos_pa_filter_out(struct damos *scheme, struct folio *folio)
 
 enum migration_mode {
 	MIG_PAGEOUT,
+	MIG_MIGRATE_HOT,
 	MIG_MIGRATE_COLD,
 };
 
@@ -375,8 +376,10 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s,
 		if (damos_pa_filter_out(s, folio))
 			goto put_folio;
 
-		folio_clear_referenced(folio);
-		folio_test_clear_young(folio);
+		if (mm != MIG_MIGRATE_HOT) {
+			folio_clear_referenced(folio);
+			folio_test_clear_young(folio);
+		}
 		if (!folio_isolate_lru(folio))
 			goto put_folio;
 		/*
@@ -394,6 +397,7 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s,
 	case MIG_PAGEOUT:
 		applied = reclaim_pages(&folio_list);
 		break;
+	case MIG_MIGRATE_HOT:
 	case MIG_MIGRATE_COLD:
 		applied = damon_pa_migrate_pages(&folio_list, mm,
 						 s->target_nid);
@@ -454,6 +458,8 @@ static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
 		return damon_pa_mark_accessed(r, scheme);
 	case DAMOS_LRU_DEPRIO:
 		return damon_pa_deactivate_pages(r, scheme);
+	case DAMOS_MIGRATE_HOT:
+		return damon_pa_migrate(r, scheme, MIG_MIGRATE_HOT);
 	case DAMOS_MIGRATE_COLD:
 		return damon_pa_migrate(r, scheme, MIG_MIGRATE_COLD);
 	case DAMOS_STAT:
@@ -476,6 +482,8 @@ static int damon_pa_scheme_score(struct damon_ctx *context,
 		return damon_hot_score(context, r, scheme);
 	case DAMOS_LRU_DEPRIO:
 		return damon_cold_score(context, r, scheme);
+	case DAMOS_MIGRATE_HOT:
+		return damon_hot_score(context, r, scheme);
 	case DAMOS_MIGRATE_COLD:
 		return damon_cold_score(context, r, scheme);
 	default:
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 18b7d054c748..1d2f62aa79ca 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1406,6 +1406,7 @@ static const char * const damon_sysfs_damos_action_strs[] = {
 	"nohugepage",
 	"lru_prio",
 	"lru_deprio",
+	"migrate_hot",
 	"migrate_cold",
 	"stat",
 };
@@ -1660,7 +1661,8 @@ static ssize_t target_nid_store(struct kobject *kobj,
 			struct damon_sysfs_scheme, kobj);
 	int err = 0;
 
-        if (scheme->action != DAMOS_MIGRATE_COLD)
+        if (scheme->action != DAMOS_MIGRATE_HOT &&
+            scheme->action != DAMOS_MIGRATE_COLD)
                 return -EINVAL;
 
 	/* TODO: error handling for target_nid range. */
-- 
2.34.1